Information Technology Reference
In-Depth Information
some cold water in the face of the Cat 7 naysayers. Not only is there a demonstrated
need for 10 GbE, but there is now a true calling for a Category 7/Class F standard.
See Chapter 11 for the full story on 10 Gb cabling.
IBM Corporation and others introduced Token-Ring networks in the mid 1980s.
The network topology is now embodied as the IEEE 802.5 standard. Token ring was
originally implemented on shielded twisted pair (STP) cable using a unique her-
maphroditic connector, commonly called the IBM data connector. This cable type
and connector is now specified in the TIA/EIA-568-C standard. More recently,
Token-Ring has been migrated to conventional unshielded twisted pair (UTP) cable
(what we simply call twisted-pair in most of this topic).
Token ring has a clever topology that allows an electrically continuous ring to be
implemented with wiring that is installed in a hubbed-star configuration. Each arm of
the star is called a
lobe
. As shown in Fig. 2.8, a special type of wiring hub, called a
multistation attachment unit (MSAU), allows signals from workstations (or from
servers or bridges) to be looped through to the next workstation, in turn, until the sig-
nal is ultimately looped back to the beginning workstation. This effectively turns the
star wiring into a loop or ring, from which the Token-Ring gets the “ring” part of its
name. The “token” part of the name comes from the fact that a so-called token is
passed from station to station, along with data, commands, and acknowledgments.
The LAN signal thus proceeds in an orderly fashion around the ring in a loop.
Here is a very simplified explanation of the process. A station may transmit only
when it “has the token.” All transmitted frames are passed from station to station
FIGURE 2.8
The multistation attachment unit (MSAU), a special type of wiring hub, is used for Token-Ring
networks.
